The delivery of proteins (e.g., therapeutic proteins) to cells is limited by a number of factors, including the poor permeability and target specificity. Protein transduction represents one emerging technology for delivering proteins into cells by exploiting the ability of certain proteins to penetrate the cell membrane. However, the majority of the proteins delivered by this method are usually trapped and subsequently degraded in the endosomes or lysosomes of the recipient cells. Another option relies on virus mediated gene delivery (gene therapy), which has been widely pursued as viruses have the unique ability to infect cells and deliver the contents in the cytoplasm efficiently. However viruses present a variety of potential problems to the patient relating to toxicity, immune and inflammatory responses, gene control and targeting tissues. In addition, the possibility of the virus becoming virulent in the patient is an added risk.
One particular agent that holds a great deal of promise as a protein-based therapeutic is the RNA-guided DNA nuclease Cas9 that can make edits (e.g., additions or deletions) to single base pairs and longer stretches of DNA (Pennisi, E. “The CRISPR Craze”. Science, 2013; 341 (6148): 833-836.). Cas9 has additionally been modified to make programmable transcription factors that allow the targeted activation or silencing of specific genes (Larson, M. H et al., “CRISPR interference (CRISPRi) for sequence-specific control of gene expression”. Nature Protocols, 2013; 8 (11): 2180-96). Accordingly, Cas9 has the potential to correct specific target genes for treating both recessive and dominant genetic diseases, offering significant advantages over traditional gene therapy approaches, which have only been useful for correcting some recessive genetic disorders. Therefore, it is of critical importance to develop methods and systems for effectively delivering protein therapeutics, such as Cas9, to their desired target cells in order to realize the full potential of protein based therapeutics.